1. Field of the Invention
The invention relates to wound dressings of alginate fiber and to the use of the dressings both for keeping a wound bed moist and for packing a deep wound.
2. Description of the Related Art
U.K. Pat. Speck. No. 653,341 (Bonniksen) which was published May 16, 1951 says: "The use of calcium alginate materials, made up into wool, gauze, foam, and the like, in surgery is now well known. They are used, because of their absorbability in the body, to control hemorrhage, fill `dead space` after the removal of organs or massive tissue, act as tissue isolating films, and externally as burn, ulcer and wound covers. They fill a recognized and important need, their properties having been described in detail by George Blaine in the Annals of Surgery for Jan., 1947" (page 2, lines 5-23). The Bonniksen specification further says that when a calcium alginate dressing is placed on an external wound, it swells in and is very slowly dissolved by the body fluids.
U.K. Pat. Spec. No. 1,394,741 (Franklin et al.) which was published May 21, 1975 says that calcium alginate materials have long been used as hemostatic surgical dressings, usually after being knitted into gauze and then replacing part of the calcium content by a more soluble cation such as sodium. Soluble cations are said to enable the alginate to disperse more readily in body fluids and tissues. A knitted alginate is currently being marketed as Ultraplast.TM. styptic gauze wound dressing by Wallace, Cameron & Co. Ltd., Glascow, Scotland.
U.S. Pat. No. 4,562,110 (Tong) says that the knitting of the dressing of the Franklin specification "has usually involved handling problems and has been carried out batchwise which is rather inefficient and uneconomic resulting in a costly and wasteful production process" (col. 1, lines 38-48). In the invention of the Tong patent, calcium alginate fiber material is first converted into the sodium/calcium mixed salt form, dried, and then "made up into a tow suitable for swab production or alginate wool or into the form of a non-woven wadding suitable for use as a medical or surgical dressing" (col. 1, lines 49-58).
The Tong patent discusses a process for making an alginate dressing as disclosed in International Pat. Appl. No. PCT/GB30/00066 (Courtaulds Ltd.) in which a tow of "calcium alginate fibres or filaments is passed in a flow of water through a spreading device, such as a device with a `fish tail` outlet, and the spread band or sheet produced is fed forwards and deposited on a liquid permeable conveyor, such as Fourdrinier wire mesh conveyor, moving at a slower speed so that the fibres are overlaid in a substantially uniform layer or sheet forming a web which is then dried to provide a unitary non-woven alginate fabric. As a result of the overlaying, the fibres become crimped or looped and cross over each other in the web so that a parallel orientation thereof is destroyed" (col. 2, lines 40-59). This produces "a dried web of intersecting fibres or filaments bonded together at their cross-over points to provide a strong unitary structure" (col. 3, lines 18-23).
The Tong patent says that the process of the Courtaulds PCT application produces "a relatively harsh fabric likely to be very stiff and to have poor handling qualities, especially if one attempts to make up such webs into thick or multilayer fabrics" (col. 5, lines 7-15). The invention of the Tong patent concerns a process similar to that of the Courtaulds PCT application except including "at least one controlled treatment step which is effective to eliminate or reduce bonding of the overlaid fibres at their points of contact or intersection" (col. 4, lines 26-33).
U.S. Pat. No. 4,421,583 (Aldred et al.) corresponds to the Courtaulds PCT application.
Although it is not known whether alginate fabrics are being manufactured in accordance with any of the above-discussed processes, a carded web of alginate fibers is being marketed as Steriseal Sorbsan.TM. surgical dressing by N. I. Medical, Redditch, Worcestershire, England, and a carded and needle-tacked web of alginate fibers is being marketed as Kaltostat.TM. haemostatic wound dressing by Cair Ltd., Aldershot, Hatt, England. Alginate tow is also marketed by each of those companies under the same tradenames for use as wound dressings, and especially for surgical packing.
Except for the knitted Ultraplast.TM. and the needle-tacked Kaltostat.TM. wound dressings, each of the aforementioned commercial alginate products has poor integrity and hence is difficult to handle. However, the needle-tacked Kaltostat.TM. wound dressing has a relatively high basis weight, about 160 g/m.sup.2, and is not as supple as would be desired for most applications. It is assumed that the needle-tacked Kaltostat.TM. dressing is not offered at lower basis weights, because it then would be rather weak. Additionally, because alginate fibers are highly absorbent, dressings based on high basis weight webs of the fibers would be more likely to desiccate a wound if applied to the wound in a dry condition. The manufacturer of the needle-tacked Kaltostat.TM. dressing avoids this problem by recommending that the dressing be moistened before application to the wound.
Except for the knitted Ultraplast.TM. wound dressing, the commercial alginate wound dressings mentioned above are weak and tend to shed fibers. Because of their weakness, skill is required to apply the dressing to wounds, and handling problems are aggravated when ones fingers are not completely dry.
Although the knitted Ultraplast.TM. wound dressing has good integrity when dry, it becomes weak and loses its integrity when saturated with saline or body fluids. This loss of integrity causes the Ultraplast.TM. wound dressing to disintegrate while being lifted from a wound (as do other commercial alginate dressings cited above), necessitating that it be picked out in tiny pieces or removed from the wound by irrigation. Because removal by irrigation is a complicated and messy process that requires a substantial degree of skill, users prefer wound dressings that can be lifted from a wound in a single piece.
While we are not aware of any rigorous clinical testing to show any medicinal effect from dressing or packing a wound with an alginate fabric, clinical testing has established that the healing of a wound is enhanced by keeping the wound moist, and alginate dressings and packings admirably retain moisture. Alginate fibers also release well from human tissue.